If it was modified by a malicious program, removing the malicious program would have solved the issue. Since there is no sign of a malicious program in your system, no need to worry about it. Like I said, this key is modified by both legitimate and malicious program. The tool does not know which program modified the key. If it sees a modification, it lists it.

Is the drive.bat file located in your USB drive? If so, you can delete it. USB vaccine disables autorun feature ergo the malware cannot spread automatically. If the data inside the USB drive is not important, I would counsel you to format it. Right-click on the USB drive and choose Format > Quick Format > OK .

Please download USBVaccineSetup.exe from Panda Software to the desktop of your clean / working computer.
Insert your USB flash drive into the clean / working computer
Double-click on USBVaccineSetup.exe to install the program
Select your language, read and accept the agreement to continue
Choose if you would like the program to run at all times, and for all newly inserted USB drives
Click Next then Finish to complete the installation, the program will launch
Select your USB drive from the list, then click Vaccinate USB note: optionally you can click Vaccinate computer as well, this disables removable items from automatically running on the system entirely
A message should appear that your USB drive was vaccinated. If not please report the error in your next post

I am inclined to believe that it is an FP. The key can be modified by both malicious and legitimate program. Since AdwCleaner cannot determine which program modified the key, it is showing it on its log.